The subject matter disclosed herein relates to hydronic air conditioning systems.
A typical hydronic air conditioning system includes several components. First, the system includes heat pumps or chillers or other systems, such as boilers, to provide a flow of hot or cold (as needed) water, which is used as the thermal energy transfer medium, to the system. Second, the system typically includes an air handling unit. The air handling unit is utilized to provide fresh air to the system, and may include a heating and/or cooling coil to treat the fresh air before it is introduced to the conditioned space. Further, the system includes a climatic beam having a heating and/or cooling coil through which hot or cold water produced by the heat pump or chiller is circulated. The pretreated fresh air is flowed through nozzles in the climatic beam and into the space to be conditioned. The treated fresh air proceeds into the room, setting up an induction cycle where ambient air from the room is urged past the coil, and recirculated into the room.
The climatic beam provides a good level of comfort mainly in cooling mode since the air velocity in the room is low. As it uses cold water at relatively high ΔT, it provides an operation energy savings at the heat pump/chiller. In cooling mode, however, the cold water has to be carefully managed in order to avoid condensation depending on the ambient air conditions (temperature and relative humidity). The climatic beam does not filter the room air recirculated through the system, so air quality is improved only by the primary or fresh air flow. A CO2 sensor can be located at the air inlet grille of the chilled beams and then can trigger the fresh airflow intake into the room as necessary to manage CO2 levels in the room. One advantage is that if nobody is in the room, the fresh airflow can be drastically reduced which generates energy savings.
In heating mode at low airflow, a stratification phenomena can occur creating discomfort when the temperature of the water circulating in the coil is too high. The stratification causes the CO2 sensor not to measure the true CO2 level of the room due to the stratification effect, thus resulting in additional potential discomfort. Similarly, stratification results in the true room temperature not being measured by a temperature sensor in the room.
The primary (“fresh”) airflow is often higher than the hygienic airflow required by the hygienic codes, which requires that air handling units are sized to match building thermal loads. The primary airflow is usually significant as it has to fit both hygienic and thermal requirements in the building and is only slightly modifiable. This significant fresh airflow requires a large duct to be installed in the building to handle the required flow. Further, the air handling unit is oversized compared to those used in other hydronic systems, as it has to fit both hygienic and thermal requirements. The air handling unit has to deliver a high static pressure in order to provide the right amount of fresh air to each of the chilled beams. The air handling unit has to operate during the night, mainly during winter time, in order to keep a minimum temperature within the building.
In a same building, the chilled beams' size (usually the length) vary depending on the expected room loads. This creates complications for HVAC and false ceiling installers.